This invention relates to microfocus X-ray tubes such as are used to take medical X-rays. In such X-ray tubes, the electron beam is focused on an extremely small point on the target, which has the medical advantage that the X-ray silhouette is very clear and crisp. However, the highly dense, small spot of electrons quickly melts the target no matter what kind of cooling device is used, and therefore either the X-ray target is consumed in one use or fewer electrons are used in the beam than would otherwise be desirable. In particular, it is highly desirable in medical X-ray work to use an extremely short exposure time so that the motion of the patient or of the patient's inside organs does not smear the picture. However, with prior-art microfocus tubes, the exposure time must be relatively long to get enough X-rays to form the picture because the rate of X-ray production is so small.
The problems suggested in the preceding prargraphs are not intended to be exhaustive, but rather are among many which tend to reduce the effectiveness of prior-art microfocus X-ray tubes. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that microfocus X-ray tubes appearing in the prior art have not been altogether satisfactory.